Alpaca Markets is a brokerage platform that provides access to financial markets through developer-friendly APIs, enabling users to trade stocks, options, and cryptocurrencies. The platform offers commission-free trading for eligible retail U.S.-listed stocks, ETFs, and options, with crypto trading subject to small fees based on volume and order type. Alpaca's Market Data API offers both free and paid subscription plans, with the free plan providing 15-minute delayed data and the paid plan offering real-time data. The platform is accessible via web browsers, allowing users to build and scale trading applications efficiently.